A welding operation includes a sputter removal process, which is considered a time inefficient process. To reduce the numbers of times of the sputter removal process, it is necessary to reduce sputtering. A well-known technique to reduce sputtering is a consumable electrode arc welding in which welding is performed by feeding a welding wire in alternating forward and backward directions and by alternating a short-circuit state and an arc state (see, for example, Patent Literature 1). The following is a description, with reference to FIG. 9, of an example of a method for controlling arc welding in which welding is performed by alternating a short-circuit state and an arc state while feeding a welding wire as a consumable electrode.
FIG. 9 shows time waveforms of a wire feed speed, a welding output, and other elements according to the conventional arc welding. As shown in FIG. 9, in a short circuit period from a time t1 when a short circuit occurs until a time t2 when an arc occurs, the wire feed speed is changed from a basic feed speed to a backward feed speed. In an arc period from the time t2 when the arc occurs until a time t6 when another short circuit occurs, the wire feed speed is accelerated to return to the basic feed speed. In the arc period, from the time t2 when the arc occurs until a time t3, which is a first predetermined time, the welding current is increased to reach a predetermined peak current IP. After reaching the predetermined peak current IP at the time t3, the welding current may be kept at the peak current IP for a predetermined period. From the times t3 until a time t4, the welding voltage is controlled to be constant, and the welding current based on the constant voltage is outputted. From the time t4, the welding current is decreased to reach a predetermined base current IB, which is lower than the predetermined peak current IP. From a time t5 until the time t6 when the arc period ends, the welding current is kept at the predetermined base current IB.
As described above, the transfer of molten metal of the wire to the base material during a short circuit is mechanically secured by feeding the wire in the backward direction. This regulates the irregular short-circuit cycle, which is the principal cause of sputtering, thereby reducing sputtering and stabilizing a short-circuit transfer welding process.
The above-described conventional arc welding mechanically secures the transfer of the molten metal of the wire to the base material during a short circuit. This regulates the irregular short-circuit cycle, which is the principal cause of sputtering, thereby reducing sputtering.
In the welding start period, however, no weld pool has yet been formed in the base material (also referred to as the object to be welded). This makes it harder to open the short circuit than in the steady-state welding period (also referred to as the main welding period) in which the base material has a weld pool. Thus, in the welding start period, it takes a longer time and a larger welding current to open the short circuit. This may cause the molten metal of the wire to grow too much, thereby generating small sputters when the short-circuit opens.